NITRIC-OXIDE REGULATES SPIKE FREQUENCY ACCOMMODATION IN NODOSE NEURONS OF THE RABBIT

A Ca2+-dependent slow spike after hyperpolarization (AHP(slow)) is pre sent in about 35% of the neurons in the nodose ganglion. Although the AHP(slow) profoundly affects spike frequency accommodation of these ne urons, the mechanisms that control the generation and the duration of the AHP(slow) are unclarified. N-omega-Nitro-L-arginine methyl ester ( L-NAME; 10 mu M), a specific inhibitor of nitric oxide synthase (NOS), reduced the AHP(slow) by more than 92%. The L-NAME block of the AHP(s low) was antagonized by application of 50 mu M S-nitroso-N-acetylpenic illamine (SNAP), a nitric oxide donor. The fast, Ca2+-dependent, spike after hyperpolarization preceding the AHP(slow) and the elevation of intracellular Ca2+ accompanying the AHP(slow) were unaffected by L-NAM E treatment. These findings indicate that products of NOS activity mig ht directly or indirectly activate the AHP(slow) K+ channels at a step beyond Ca2+ influx or intracellular Ca2+ mobilization.